wow, a 75%-80% drop on an extremely white-hat site. No link building, no spam nothing, just evergreen content. This makes it a 95% drop compared to last year as Bing and other stay the same.
Another site of mine gets an absolute max traffic each day, in the dozens a day from over 2000 pre-Panda. I almost get the same from DuckDuckGo as I get from Google. I'm positive it's not my site, Bing brings me many times more than Google. My major competitors have also gone down in referrals, so it maybe more ads/ad clicks or Google display changes, not just seo.
We need to get ready for absolutely no Google traffic, unless you're a major brand or you pay for traffic via Adwords. Google controls every aspect of traffic, no SEO is going to help